USPTO Patents Application 09913423

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PCT/PTO 18AUB20M
09/913423

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Electric machine

An electric machine with a rotor which is rotatably mounted in a housing with a rotor shaft
which extends beyond the housing, a plurality of electromagnet components which are
statically disposed in the housing at uniform angular spacings and spaced from the axis of
rotation of the rotor, each with a coil core bearing a coil winding consisting of one or more

are non-rotatably retained in or on the rotor, these permanent magnets each having a pole
face aligned opposite the end faces of the coil cores and each having a polarity which is
successively reversed in the peripheral direction, wherein the coil cores of the electromagnet
components are disposed parallel to the axis of rotation of the rotor shaft in the interior of the
housing in such a way that their opposing end faces each lie in two planes which are spaced
from one another and extend at right angles to the axis of rotation of the rotor shaft and the
ends of the electric conductors which form the coil winding of the individual electromagnet
components are interconnected via an electric or electronic control device to form at least
two pairs of electrical connections and the rotor has at least two outer armature discs which
extend radially to before the end faces of the coil cores and in which the permanent magnets
are retained with their pole faces aligned with the respective associated end faces of the coil
cores, the radially inner region of the said armature discs being provided with holes.

Such machines which can be connected to electric current sources are used for example as
wheel hub motors for vehicle drives because of the favourable power-weight ratio. In this
case these motors are designed so that the permanent magnets are retained in a disc, which is
made from non-magnetic material and is non-rotatably connected to the rotor shaft, in such a
way that their pole faces open freely on both sides into the flat sides of the disc-shaped rotor
armature, the magnets being disposed so that in the peripheral direction successive pole faces
on the same side of the armature have alternating polarities. The electromagnet components
in the form of coils wound on metal cores are disposed on the inner faces of the housing
cover or radial housing walls facing the disc-shaped rotor armature at a distance
corresponding to the average radial distance of the permanent magnets from the axis of
rotation of the rotor shaft. The control of these coils is achieved preferably by an electronic

conductors and with permanent magnets which are disposed at uniform angular spacings and

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control device which generates a magnetic rotating field, so that the control of contacts
sliding on a commutator, which is basically also conceivable but is susceptible to wear, is
omitted. Such electronically controlled machines are also designated as brushless disc
armature machines (GB 2 275 371 A). Furthermore, brushless disc armature machines are
also known in which the rotor has two outer armature discs which extend radially to in front
of the end faces of the coil cores which are fixed on the housing, the permanent magnets
being retained in these armature discs with their pole faces aligned with the respective
associated end faces of the coil cores (e.g. DE 197 01 797 A, Figure 18; DE 42 14 483).

The object of the invention is to improve the efficiency of the known electric machines and
to minimise any decline in the power due to reduction of the magnetisation of the permanent
magnets over the course of time. At the same time the machines should be economical and
simple to produce and should have a favourable unit weight.

Starting from an electric machine of the type mentioned in the introduction, this object is
achieved according to the invention in that in each case pairs of legs, which succeed one
another in the peripheral direction and are each provided with a pole face of different polarity
on the free end facing the coil, of the permanent magnets provided in the two opposing outer
armature discs are connected to one another in the end regions remote from the pole faces by
a respective yoke which encloses the magnetic field and is made from soft or hard magnetic
material, that the armature discs are connected to one another by radially extending walls
which form the cavity between the armature discs into a plurality of chambers which are
offset with respect to one another in the peripheral direction and are open towards the
electromagnet components, and that the radially inner holes provided in the armature discs
each open into the chambers of the rotor. The permanent magnets which are associated with
the electromagnet components disposed centrally between both armature discs and thus are
rigidly fixed on the peripheral wall of the housing of the machine are constructed in the
manner of horseshoe magnets by means of the yokes which in each case connect two single
magnets which succeed one another in the peripheral direction, resulting in a construction of
the motor in which the magnetic field of the permanent magnets is kept contained as far as
possible within the magnetic material of the permanent magnets, connected by the yoke, of

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the coil core, so that a low magnetic leakage field can be produced only in the narrow air gap
between the end faces of the coil cores of the electromagnet components and the pole faces
of the electromagnets. Losses of the magnetic rotating field generated in the electromagnetic
components when the machine is switched on as motor are therefore minimised. This also
applies when the machine is used as generator, which suggests itself for example for wind
generators in which a direct coupling of the axis of rotation of the rotor to the output shaft of
the wind wheel is possible without connection of a reduction gear between them. In addition
to the favourable electric efficiency of the generator, the mechanical losses in the
transmission gear are also avoided. In this case the radially extending walls which connect
the armature discs act like the blades of a fan, i.e. via the radially inner holes in the armature
discs air is drawn out of the housing and is blown radially outwards between the
electromagnet components as a cooling air stream.

In the simplest case a row of electromagnet components is provided in the interior of the
housing of the machine, and then the rotor has two outer armature discs guided on opposing
sides in front of the coil core end faces of the electromagnet components.

The power of the machine can be increased without increasing the diameter in that two or
more rows of electromagnet components spaced from one another in the longitudinal
direction of the rotor shaft are disposed in the interior of the housing, wherein in addition to
the two outer armature discs which are guided in front of the outer end faces of the coil cores,
pointing in opposite directions, of the outermost rows the rotor has an additional armature
disc with permanent magnets guided into each space between adjacent rows of electromagnet
components in front of the end surfaces thereof which face one another, and the pole faces of
differing polarity of the permanent magnets which are each exposed on opposing sides of the
respective additional armature disc are aligned in the radial direction with the end faces of
the coil cores of the rows of electromagnet components. Thus the permanent magnets
disposed in the additional armature discs are - unlike the permanent magnets in the outer
armature discs - constructed not as horseshoe magnets but as bar magnets of short length in
order thus to keep the air gaps small between the pole faces of these magnets and the facing

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end surfaces of the coil cores of the electromagnet components and thus to avoid losses due
to magnetic leakage fields.

In this case the interior of the housing is advantageously closed off and sealed against the
external atmosphere, this sealing being achieved in the region of the shaft of the machine
extending beyond the housing by a corresponding seal. The air drawn in from the housing
through the radially inner holes in the armature discs and blown through between the
electromagnet components takes up heat from the coils of the electromagnet components.
Over the outer periphery of the armature discs the circulated air then passes into the space
between the rotor and the end walls of the housing and is drawn back to the radially inner
holes. In this way a self-contained air flow is produced in the interior of the housing and
acts upon not only the electromagnet components but all other exposed surfaces in the
interior of the housing and prevents the occurrence of locally higher temperatures (hot spots).

For removal of the heat produced in the machine and given off into the circulated air it is
recommended that the outer and/or inner face of the housing be provided with ribs in order
enlarge the surface of the housing which gives off or takes up heat. In this special case it
may be advantageous if radially extending ribs are provided on the inner faces of the housing
end walls facing the rotor and between these ribs radial channels are formed for the return of
the gaseous atmosphere circulated in the interior of the housing.

Moreover the radial channels can be closed off on the armature disc side by a metal plate so
that between the radial ribs channels are produced which are open only on the radially inner
and radially outer end and are connected to the interior of the housing and through which the
circulated air is returned.

The cooling of the electric machine according to the invention can also be carried out by
through flows of ambient air, in that air inlet openings are provided in regions of the housing
lying opposite the holes in the armature discs and air outlet openings which are offset radially
outwards are provided in the housing.

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In this case the electromagnet components are disposed at uniform spacings in the peripheral
direction and protrude from the inner face of the peripheral housing wall into the space
formed between the armature discs.

An embodiment in particular of the machine of the type mentioned in the introduction may
be advantageous in which each pole face of the permanent magnets has in the peripheral
direction an extent which covers two pole faces of the coils of two electromagnet
components which succeed one another in the peripheral direction, and that the control
means is designed so that in order to drive the rotor this control switches over the polarity of
every second one of the electromagnet components which succeed one another in the
peripheral direction with each rotation of the rotor about an angular spacing which
corresponds to the angular spacing between two electromagnet components which succeed
one another in the peripheral direction. This results in a 2 -phase machine.

Alternatively three pole faces of the coils of three electromagnet components which succeed
one another in the peripheral direction can be associated with each pole face of the
permanent magnets, in which case the control means is designed so that in order to drive the
rotor, after the rotor has rotated by an angular spacing corresponding to the angular spacing
between electromagnet components which succeed one another in the peripheral direction,
the control means switches over the polarity of every third one of the electromagnet
components which succeed one another in the peripheral direction and thus a 3 -phase
machine is produced.

Basically more than three pole faces of the coils of electromagnet components which succeed
one another in the peripheral direction can be associated with each pole face of the
permanent magnets, in which the case the control means is designed so that in order to drive
the rotor, after the rotor has rotated by an angular spacing corresponding to the angular
spacing between electromagnet components which succeed one another in the peripheral
direction, the control means successively switches over the polarity of every one of the
electromagnet components, which succeed one another in the peripheral direction, of the
group of electromagnet components associated with a permanent magnet.

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By interconnection in each case of the coils of groups, which succeed one another in the
peripheral direction, of electromagnet components which are associated in each case with a
permanent magnet, the construction costs of the power electronics controlling the polarity of
the coils relative to individual control of each individual coil are markedly reduced. Thus the
electric control circuit in a 2-phase machine is also reduced to a 2-phase inverter control with
variable amplitude and frequency. The four coils of four electromagnet components are
located between two opposing horseshoe-shaped magnet segments. The first and the third
coils are switched over simultaneously and in the next step the second and the fourth coils are
switched over. The polarity of the first and third as well as of the second and fourth coil are
opposed. The first and third as well as the second and fourth coil can therefore be firmly
wired to one another, since the third and fourth coil are each controlled in mirror image to
the first and second coil. Thus it is possible in practice to produce a 4~phase control with a 2-
phase control.

The direction of rotation and the speed of the motor can be determined in that the switch-
over point for the coils for switching over from one polarity to the other is controlled by way
of a position pick-up which senses the relative rotational position of the rotor in the housing.
Therefore the switch-over point for the control of the coil is determined by the sensor which
predetermines the frequency. In this case the switch-over frequency is not identical to the
motor speed, but it applies for one magnet segment. If the motor consists of ten segments
with two switch pulses per phase and segment, then the switching frequency is 20 times the
motor speed.

In this case a contactless sensor, particularly an optical sensor, which senses the relative
rotational position of the motor with respect to the housing is provided as position pick-up.

The electromagnet components can each be advantageously held on separate support
elements which can each be installed in an associated opening the in the peripheral wall of
the housing in such a way that the pole faces of the coils of the electromagnet components
are in the prescribed assembly position in alignment with the pole faces of the permanent

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magnets between the armature discs. In the event of damage to or failure of the coil of
individual electromagnet components, these electromagnet components can then be removed
individually and repaired or replaced by new electromagnet components which are capable of
functioning.

Alternatively the pre-installed arrangement of the electromagnet components in an annular
mounting, which in turn is held in the interior of the housing, is also conceivable. However,
this construction presupposes the possibility of separate installation of at least one of the
armature discs of the rotor.

The electromagnet components can each also have two separate coils with opposed
directions of winding, i.e. reversed-polarity differential windings, which can then be
selectively controlled by an electric or electronic control device. In this way the polarity of
the respective electromagnet components is reversible - depending upon the control of the
respective coil winding.

If the machine according to the invention is to be used as a generator, the ends of the
electrical conductors of each electromagnet component which form the coil winding are
advantageously connected to the input connections of a separate rectifying circuit, and the
rectifying circuits are then interconnected on the output side to a pair of electric bus lines.
The direct current made up of the sum of the direct currents generated in the individual coils
via the respective associated rectifying circuit can then be tapped from the bus line. This
embodiment is recommended particularly when the generator is driven at alternating speeds,
such as may be the case for example with electric current generation using wind power in
wind generators with rotor blades without blade adjustment due to differing wind speeds and
wind strengths.

Then in an electronic inverter circuit which is connected downstream the direct current
generated by such a generator can be converted into an alternating or three-phase current
which is synchronised with the power supply.

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The invention is explained in greater detail below in the following description of
embodiments in conjunction with the drawings, in which:

Figure 1 shows a longitudinal central section through the axis of rotation of the rotor shaft of
a first embodiment of an electric machine according to the invention with a row of
electromagnet components and two outer armature discs;

Figure 2 shows a longitudinal central section, corresponding in the sectional orientation to
Figure 1, through a second embodiment with two rows of electromagnet components spaced
from one another in the longitudinal direction and additionally with a central armature disc
provided between the two rows of electromagnet components;

Figure 3 shows a sectional view of the electric machine according to Figure 1, viewed in the
direction of the arrows 3-3 in Figure 1;

Figure 4 shows a sectional view through the rotor of the electric machine shown in Figures 1
and 3, in the sectional plane corresponding to Figure 3;

Figure 5 shows a sectional view through the rotor, viewed in the direction of the arrows 5-5
in Figure 4; and

Figure 6 shows a schematic circuit diagram of an electromagnet component which can be
used in the electric machine according to the invention, in a special construction with two
separate coil windings with opposed directions of winding which are placed on the coil core,
these coil windings being selectively controllable by an electronic control device and thus
capable of being switched over selectively in polarity.

embodiment of an electric machine according to the inventionvwhich is designated as a
whole by 10 can basically be used as a motor or generator. In the special case the machine 10
has a housing 12 which is relatively short in the axial direction and is composed of two disc-
like housing end walls 14a, 14b of relatively large diameter and the actual peripheral housing

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wall 16 which is practically shaped into a cylindrical ring of relatively short length. The
housing end walls 14a, 14b and the peripheral housing wall 16 are connected to one another
by screws or other fixing means - not shown - so as to be capable of being dismantled, and
in order to simplify assembly and dismantling of the machine 10 the peripheral housing wall
16 can also be divided in a parting plane running through the longitudinal central axis of the
housing into two peripheral wall halves which can be screwed to one another or can be
connected to one another in some other way.

A bearing receptacle 20 for a radial bearing 22 is formed in each of the end walls 14a, 14b
and a shaft 24 passing through the housing end wall 14a is rotatably mounted in these
bearings.

In the radially outer regions of the armature discs 26a, 26b permanent magnets 27 are
retained so that they succeed one another in the peripheral direction at uniform angular
spacings, and the pole faces of these permanent magnets which face inwards, i.e. towards the
respective opposing armature disc 26b, 26a, have a polarity which is successively reversed in
the peripheral direction. Also the pole faces, which lie opposite one another in the axial
direction, of the permanent magnets 27 of the two armature discs have different polarities.
The permanent magnets 27 are retained in recesses in the armature discs 26a, 26b, whereby
permanent magnets 27 which succeed one another in the peripheral direction are interlocked
to form a horseshoe magnet in each case by connection of their end faces remote from the
coil by means of a yoke made from hard or soft magnetic material largely enclosing a
magnetic field.

Electromagnet components 28, each having a coil core 32 bearing a coil winding 30
consisting of one or more conductors, are disposed on the inner wall of the peripheral
housing wall 16 - likewise at uniform angular spacings. The ends of the conductors of the
coil winding 30 are connected to an electronic control device by which the electric current
delivered to the control device from an electric current source is fed into the coils 30 in a
controlled manner in such a way that in the electromagnet components 28 a magnetic
rotating field is generated which in interaction with the permanent magnets 27 disposed n the

armature discs 26a, 26b results in a relative rotation of the rotor and thus of the shaft 24 with
respect to the housing 12. Thus in conjunction with the aforementioned electronic control -
not shown - the electric machine according to Figure 1 constitutes a brushless electric axial
field motor which can be driven by a direct current source. When conversely the shaft 24 is
driven, an electric rotating field is generated by the permanent magnets 27 in the
electromagnet components 28 rotating with the armature discs (26a, 26b), and this field can
be tapped at the ends of the coils 30 of the electromagnet components 28 and used as direct
current by a suitable rectifying circuit. The electric rotating field can alternatively be
converted into rotating or alternating current by corresponding electronic control means.

Figure 2 shows an embodiment of the an electric machine according to the invention which is
designated as a whole by 10' in which the power is increased without increasing the diameter
in that two rows of electromagnet components 28 which are spaced from one another are
disposed in the interior of the housing 12 in the longitudinal direction of the rotor shaft. In
addition to the two outer armature discs 26a, 26b which are guided in front of the outer end
faces of the coil cores, pointing in opposite directions, of the electromagnet components 28
the rotor has a third armature disc 26c additionally guided into the space between the two
rows of electromagnet components 28. Permanent magnets 27 are set in this central armature
disc 26. In this way the air gaps between the pole faces of the permanent magnets 27 and the
end surfaces of the coil cores 32 of the electromagnet components 28 in the central armature
disc 26c can be kept small and thus losses due to magnetic leakage fields are avoided. Here
too the peripheral housing wall 16 is again divided along a central plane for assembly
reasons.

Apart from the second row of electromagnet components 28 disposed offset in the axial
direction and the arrangement of the additional central armature disc 26c, the machine
corresponds functionally to the aforementioned electric machine described in connection
with Figure 1, so that with regard to the construction of the electric machine 10' it is
otherwise sufficient to refer to the preceding description of the machine 10, since
components of the two machines which are functionally the same are assigned the same
reference numerals in the drawings.

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lt can be seen that a further increase in power without an increase in diameter is possible by
arrangement of one or more further axially offset rows of electromagnet components between
each of which an additional armature disc with permanent magnets is disposed.

From the sectional view shown diagrammatically in Figure 3 of the electric machine shown
in Figure 1 it can be seen that from the peripheral wall 16 of the housing 12 electromagnet
components 28 - twenty-four in all in the illustrated case - are disposed in uniform
distribution and offset with respect to one another in the peripheral direction.

The shaft 24 bears - as mentioned - the rotor which is retained non-rotatably on it and is also
shown separately in Figures 4 and 5, this rotor having the two armature discs 26a, 26b made
from non-magnetic material which are spaced from one another and extend radially into the
vicinity of the peripheral housing wall 16 and in which are disposed the permanent magnets
27 which succeed one another in the peripheral direction and are held at uniform angular
spacings, and in fact in the present case there are twelve permanent magnets in all, of which
the pole faces which face inwards, i.e. towards the respective opposing armature disc 26b,
26a) have polarities which are successively reversed in the peripheral direction. Also the
pole faces, which lie opposite in the axial direction, of the permanent magnets 27 of the two
armature discs 26a, 26b have different polarities. In the illustrated embodiment each pole
face of a permanent magnet extends in the peripheral direction over two pole faces of the coil
cores 32 of electromagnet components which succeed one another in the peripheral direction.

The ends (not shown) of the conductors of the coil winding 30 of the electromagnet
components extend beyond the housing and are then connected in a suitable manner to the
electronic control device already mentioned by which the electric current delivered from an
electric current source is fed into the coils of the electromagnet components in a controlled
manner in such a way that the electromagnet components 28 generate the magnetic rotating
field which in interaction with the permanent magnets disposed on the armature discs 26a,
26b results in the rotation of the rotor and thus of the shaft 24.

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The armature discs 26a, 26b are each disposed on the outer end surfaces of a hub body 36
(Figures 4 and 5) from which radial walls 38 protrude into the space between the armature
discs 26a, 26b, the radial extent thereof being chosen such that the electromagnet
components 28 protruding radially inwards from the peripheral housing wall 16 can still
enter radially into the space between the armature discs 26a, 26b without butting against the
radially outer ends of the radial walls 38 projecting from the hub body 36. Between each pair
of radial walls 38 of the hub body 36 which succeed one another in the peripheral direction
there are additionally provided radial walls 38 f which are fixed on the inner faces of the
armature discs 26a, 26b which face one another, so that a row of chambers 40 is formed
which succeed one another in the peripheral direction, these chambers being closed off
internally by the hub body 36 and laterally by the armature discs 26a, 26b respectively.
Immediately above the hub body 36 inner holes 46 which lead into the chambers 40 are
provided in both armature discs 26a and 26b. Thus with the rotor rotating air can pass via the
holes 46 out of the interior of the housing and into the chamber 40 and is accelerated radially
outwards there by the centrifugal force of the rotating rotor. This air flowing radially
outwards then leaves the chambers 40 and encounters the electromagnet components
projecting from the peripheral wall 16 of the housing 12 into the space between the armature
discs 26a, 26b and passes through the spaces between these components, flows around them
and can then pass beyond the peripheral surface of the armature discs again and into the
space between armature discs 26a, 26b and the housing end walls 14a, 14b. Thus the rotor
formed by the hub body, the radial walls 38 and 38' and the armature discs 26a, 26b
simultaneously constitute the impeller of a fan which effects a forced circulating flow of the
air enclosed in the housing or - in special cases - of a gas filling introduced there. As soon
as the temperature in the forced circulating flow rises above the ambient temperature, heat is
removed via the housing, i.e. the peripheral housing wall 16 and the housing end walls 14a
and 14b, to the external atmosphere. The provision of ribs on the surfaces of the housing
promotes not only the transfer of heat from the forced circulating flow in the interior of the
housing to the housing but also the emission of heat from the housing to the surrounding
atmosphere. Instead of the forced circulating flow in the interior of the housing, cooling with
external air can also take place if air inlets are provided in the housing end walls 14a and 14b
approximately in alignment with the holes 46 in the armature discs 26a, 26b and outlet

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openings are provided in the peripheral housing wall 16 in the region between the
electromagnet components 28.

Figure 6 shows schematically the circuit of an electromagnetic component 28 of a special
construction of the electromagnet components in which the coil core bears two coil windings
30a and 30b which are wound in opposing winding directions one above the other. It can be
seen that the ends of the two coil windings 30a, 30b are connected to the same current
conductor, whilst the other ends of the two coil windings are each connected to separate
conductors leading to an electronic control unit EC by means of which the second current
conductor can be selectively switched to the first coil winding 30a or the second coil winding
30b.

With regard to the illustration of the coil winding in Figure 6 it should also be pointed out
that only half of the coil winding 30a is shown here in order to be able to show the upper part
of the coil winding 30b lying below it. In practice the winding 30a extends over the entire
length of the coil core 32. In such a case this is also referred to as a reversed-polarity
differential winding.

It can be seen that within the scope of the inventive idea modifications and variants of the
described embodiments of the electric machine 10 or 10* are possible.

When the electric machine 10 is driven as an electric motor, instead of the rotary power take-
off via the shaft 24 assumed in the description, as an alternative the shaft 24 can also be fixed
via a suitable flange to a rigid component. When the motor is supplied with current the
housing 12 is then set in rotation. In this embodiment the electric machine can be used as a
wheel hub motor for driving vehicles directly on the wheels. In order that the electromagnet
components 28, which in this case would rotate with the housing 12, do not have to be
controlled via sliding contacts or brushes with electric current, the arrangement of the
permanent magnets 27 and the electromagnet components 28 is advantageously exchanged,
i.e. the electromagnet components are disposed in the rotor which is now held non-rotatably
on the fixed shaft, whilst the permanent magnets 27 are disposed on the inner faces of the

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housing, i.e, the inner faces of the housing end walls 14a, 14b. In practice this is then a
kinematic reversal of the electric machine 10. The current supply to the electromagnet
components then takes place via supply lines which are laid firmly in the shaft.

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